German Offenlegungsschrift DE-OS No. 29 29 428 (corresponding to European Pat. EP-PS No. 0 022 933) discloses such a type of bearing having a sliding block with different guide channels provided as the guide channel in which there is a mandatory guidance and fixing into position of the actuating lever made possible in a deflected position. In this manner the actuating lever may be swivelled horizontally in one or another direction in a guide channel, so that in each instance, insertion of the actuating rod of a pneumatic spring is achieved. By this means also, it is possible each time to effect a separate alteration of the inclination of the seat or of the back-rest. In order to render the seat and the back rest freely tiltable and thus to nullify the arresting action of the pneumatic spring concerned, the actuating lever may be shifted upwards in a vertical channel of the sliding block and elastically engaged in position. In this location, the appropriate sections of ring which are formed on the actuating lever and which are in contact with the intermediate levers will push these intermediate levers apart in a scissors-like action, so that both actuating pins are pushed into the corresponding pneumatic springs. Since the actuating lever is locked into this position, the actuating rods remain opened, so that the seat and the back-rest may be tilted back and forth--against the existing gas pressure in the pneumatic spring. Since the ring formed on the actuating lever surrounds the chair support column, it is not possible to alter the position of the pneumatic spring forming this chair column. In a practical embodiment, a separate actuating lever is provided for this purpose. Moreover, it is not possible to selectively arrest the actuating rod in the pushed-in position solely for the back-rest pneumatic spring or for the seat pneumatic spring. U.S. Pat. No. 3,837,704 discloses a chair having its support column formed from a length-adjustable pneumatic spring and having an incline-adjustable back-rest controlled by a pneumatic spring, so that by means of an actuating lever which may be swivelled only horizontally and vertically it is possible selectively to adjust the length of the support column or the incline of the back-rest. In this case it is not possible to adjust the slope of the seat, nor is provision made for arresting the actuating rod in its pushed-in position.
A similar solution of the problem is known from the Swiss Pat. No. 563 753.